There is known an exhaust gas reflux apparatus in which the intake air is diluted by refluxing a part of the exhaust gas into the intake system of an internal combustion engine, and the propagation speed of the flame and the highest combustion temperature are decreased, thereby reducing the amount of NOx in the exhaust gas. In such an apparatus, the reflux quantity of the exhaust gas is controlled by an EGR regulating valve.
This EGR regulating valve is made operative using the negative pressure of the intake passage, and controls the reflux quantity in accordance with the operating state of the engine.
However, for example, when the engine experiences a high load operating state involving a high rotational engine speed, the temperature of the exhaust gas which is refluxed also becomes high. Thus, the EGR regulating valve deteriorates such that its function is lost or decreased due to burning of the valve portion and/or melting-loss of the diaphragm and the like as caused by the high temperature of the exhaust gas. Thus, the control of the reflux quantity of the exhaust gas becomes inaccurate, causing a situation such that the amount of NOx cannot be reduced. In addition, the high load operating state, wherein the temperature of the exhaust gas becomes high, can also be caused at a low rotating speed of the engine.